This invention relates to propulsion arrangements for Small Waterplane Area Twin Hull (SWATH) vessels.
Conventional propulsion arrangements for SWATH vessels are generally shaft-driven propeller systems receiving power from electric or other power sources located inside the vessel by way of shafts which extend through the hull of the vessel. The drive shaft for such systems usually passes through the vessel's hull at a rake angle in order to facilitate the layout of the vessel's propulsion plant equipment due to the typical hull geometry. Such angled shafting reduces propeller efficiency and often causes the propeller to protrude far beyond the hull of the ship making it susceptible to blade hits. Maintenance work to repair resulting bent or broken propeller blading or shafting is costly and requires dry dock facilities. In addition, severe blade hits can cause shaft or drive train damage which would require cuts into the hull or extensive engine room disassembly to repair and could even result in the loss of the ship at sea as a result of flooding or lack of maneuverability. Pump jets have recently been used to address some of the foregoing shortcomings of conventional systems. However, they do not address all of the shortcomings, nor do they offer any potential for improved overall efficiency.
The Hall et al. U.S. Pat. No. 5,301,624 discloses a SWATH vessel having a propeller at the rear of each pontoon which is driven by a shaft connected to an engine within the SWATH vessel. The Walters U.S. Pat. No. 4,936,237 discloses a dual hull vessel having a propeller housing mounted at the rear of each hull containing a propeller driven by a shaft extending into the hull.
The Veronesi et al. U.S. Pat. No. 5,252,875 discloses a pod-type shrouded propeller arranged to be affixed to the outside of a hull. The Pierro U.S. Pat. No. 3,708,251 shows a similar pod arrangement for a shrouded propeller. In the Taylor et al. U.S. Pat. No. 4,831,297 a submersible electric propulsion motor is described in which the propeller is integrated with a motor rotor.
The Rieben U.S. Pat. No. 5,679,037 shows a water craft having propeller housing portions on each side of the hull containing a stationary screw induction structure leading from an inlet to a propeller at the rear of the housing. According to the Garis, Jr. U.S. Pat. No. 5,078,628, a propulsor for marine vessels contains a rotor which is journaled in the hull of the vessel and has blades which extend outside the vessel's hull and are surrounded by a shroud to protect the blades. The rotor blades which project from the hull are driven by an electric motor mounted inside the hull. Stationary blades are positioned ahead of and following the rotating blades.